1. Field of the Invention
In this description of the invention and the background thereof, pulsed doppler radars are utilized as an example because they are very common and well known, and the description of the present invention in conjuction therewith is relatively clear and simple. In general, pulsed doppler radars transmit pulses of coherent radio frequencies into a region under observation. These pulses are reflected by the objects in the region ad each object changes the frequency of the reflected pulse in dependence on the velocity of the object relative to the radar, as governed by the Doppler principle. Generally, objects which are moving relative to the ground in the region of observation are targets and signals reflected from the ground, i.e., trees waving in the wind, waves in water, clouds, etc. are commonly referred to as clutter. It is necessary that the clutter signals be discriminated against with a minimum deterioration in the effectiveness of the radar in detecting targets.
1. Description of the Prior Art
Many of the prior art detectors utilize a variable or floating threshold which measures the approximate amplitude of the clutter and maintains a threshold slightly above the major portion of the clutter. In this fashion, most of the clutter signals are eliminated and only the high amplitude signals are passed to the remainder of the circuitry.
In some radar apparatus two thresholds are utilized, e.g., U.S. Pat. No. 3,828,348, entitled "System for Minimizing Multiple Time Around Echos in a Coherent-On-Receive-Doppler Radar", patented Aug. 6, 1974, but the test for passing the signals is coherent/noncoherent. Others, e.g., U.S. Pat. No. 3,707,718, entitled "Radar System", issued Dec. 26, 1972, utilize clutter trackers to actually track the clutter and suppress it so that the targets may be recognized. All of these prior art systems still allow many false signals and are susceptible to tracking clutter or losing targets in clutter.